Extractor roll drive

ABSTRACT

A continuous casting apparatus of the type wherein liquid ferrous metal is received at the inlet end of a mold and the cast bar is withdrawn in intermittent withdrawal motions from the exit end of the mold. The successive withdrawal motions are at speeds in excess of that at which the molten metal solidifies against the rear face of the bar, so that on each withdrawal an initially independent and separate new section is formed behind the withdrawing bar, with the freezing progressively taking place in the same direction as bar withdrawal. The new section later freezes against the rear face of the formed bar during the dwell period between the intermittent withdrawal motions, so that on each successive withdrawal motion the newly formed section adheres to and becomes a part of the withdrawn bar. In accordance with the present invention, the bar-withdrawing roll, which is spaced from the rear face of the bar, has a brake affixed thereto. The brake reaction force is taken up by a pendulously suspended unit having a depending ear which oscillates between an adjustable stop engaged when the roll rotates in the reverse direction and a spring-biased detent backed up by a fixed stop when the roll rotates in the bar-withdrawing or forward direction. The roll drive mechanism is arranged to impart a slight reversed roll motion during the dwell period. It has been found that without the brake unit the apparatus operates unreliably and erratically, especially after some usage, but with the brake arrangement (and the incident instantaneously applied reverse force over a predetermined distance when the forward bar movement stops) the continuous casting apparatus operates reliably and effectively over a prolonged period of time.

United States Patent [1 1 Williams et al.

[ 51 Oct. 15, 1974 EXTRACTOR ROLL DRIVE [75] lnventors:- Robert G. Williams, Birmingham;

Richard M. Coolidge, Lansing, both of Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Aug. 20, 1973 [21] Appl. No.: 389,559

[52] US. Cl. 164/282, 164/260 [51] Int. Cl 322d 11/12 [58] Field of Search 164/282, 277, 279, 83, 164/260, 273

[56] References Cited UNITED STATES PATENTS 3,258,815 7/1966 Reinfeld 164/260 3,438,426 4/1969 Parfit 164/282 Primary ExaminerJ. Spencer Overholser Assistant ExaminerJohn S. Brown Attorney, Agent, or FirmGeorge A. Grove [5 7 ABSTRACT A continuous casting apparatus of the type wherein liquid ferrous metal is received at the inlet end of a mold and the cast bar is withdrawn in intermittent withdrawal motions from the exit end of the mold. The successive withdrawal motions are at speeds in excess of that at which the molten metal solidifies against the rear face of the bar, so that on each withdrawal an initially independent and separate new section is formed behind the withdrawing bar, with the freezing progressively taking place in the same direction as bar withdrawal. The new section later freezes against the rear face of the formed bar during the dwell period between the intermittent withdrawal motions, so that on each successive withdrawal motion the newly formed section adheres to and becomes a part of the withdrawn bar. in accordance with the present invention, the bar-withdrawing roll, which is spaced from the rear face of the bar, has a brake affixed thereto. The brake reaction force is taken up by a pendulously suspended unit having a depending ear which oscillates between an adjustable stop engaged when the roll rotates in the reverse direction and a spring-biased detent backed up by a fixed stop when the roll rotates in the bar-withdrawing or forward di rection. The roll drive mechanism is arranged to impart a slight reversed roll motion during the dwell period. It has been found that without the brake unit the apparatus operates unreliably and erratically, especially after some usage, but with the brake arrangement (and the incident instantaneously applied reverse force over a predetermined distance when the forward bar movement stops) the continuous casting apparatus operates reliably and effectively over a prolonged period of time.

5 Claims, 7 Drawing Figures mamas SHEH 1 OF 3 spmaasa PATENIE U x 5 2974 PATENTED I W4 SHEEF 3 3 EXTRACTOR ROLL DRIVE This invention relates to an improved continuous casting apparatus wherein the cast bar is pulled forwardly intermittently and in which the bar withdrawal roll spaced from the mold is spring-biased in the reverse direction over a predetermined amount of reverse movement starting at the instant the dwell period starts.

In one form of continuous casting, molten ferrous metal is discharged from a holding vessel into a mold. The cylindrical walls of the mold are cooled so that the molten metal is solidified when allowed to dwell against them, thus forming a new, initially separate, bar section with a solidified annular rear end face and a cylindrical shell during each dwell period. The net heat transfer from and to the downstream annular face of the mold is such that freezing of metal takes place up to an intermediate radius between the most inboard portion of the annular face and the outer periphery of the exposed portion thereof. The frozen or solidified metal issues in bar form through an appropriate exit channel from the mold. To provide the necessary bar withdrawal, a barwithdrawing roll engages the bar at a point spaced from the point of bar issuance. This roll is rotated in a series of intermittent short bar-withdrawing rotations separated by substantial periods of bar dwell. The rotations may, for example, advance the bar a distance of about three-fourths of an inch and occur at a repetition rate of, for example, about 120 withdrawals per minute. The rate of bar withdrawal during each such movement is more rapid than the-rate of freezing of the molten metal when it flows forwardly and radially outwardly against the cylindrical mold walls. Thus, while the bar is being withdrawn and liquid metal behind it is freezing to form a new bar section, the new section is separated from the previously formed bar by a section of unsolidified metal. The molten metal forming the new bar section freezes first at the rear end of what will be the new bar section and then towards the front end of that section. Thus the direction of freeze is in the same direction as the bar is withdrawn during the bar-withdrawing periods. By the time the bar dwell period ends, the front end of the new section welds against the withdrawn rear annular end face of the previously cast section so that the new withdrawal movement (imparted in tension by the remotely located roll) draws the newly frozen section forwardly forming the rear end of the frozen bar, completing the cycle.

Desirably, the bar-withdrawal roll is spaced some distance. such as 8 to 10 feet or more, from the end of the bar against which the new metal must weld or freeze during the dwell period. It has been found that it is necessary to impart a slight reverse movement to the barwithdrawal rolls during the dwell period. Otherwise there is a tendency of the weld between the annular face of the rear end of the bar as withdrawn and the forward end of the newly frozen section of bar to break. This is a troublesome and sometimes disastrous event, since it at least requires interrupting production and may entail a time-consuming start-up operation or even may cause liquid metal to be discharged freely through the mold and onto the floor. The amount of this reverse motion is small. It may, for example, be of the order of one-fortieth of an inch. Experience with actual continuous casting operations has shown that while the apparatus. when initially placed in operation may operate with some reliability, after a period of time the operation becomes erratic and unsatisfactory with respect to bar breakage. While the cause of this is not entirely known, it is believed to be due to otherwise unnoticeable wear in the drive apparatus too slight to be significant in any other respect. In any event, it has been found that the difficulty is overcome by the apparatus herein described, which is effective, starting at the instant the bar-withdrawing motion of the withdrawal roll stops, to spring bias the roll in the reverse direction for a predetermined amount of reverse rotation.

It is, therefore, a general object of the present invention to provide an improved continuous casting apparatus of the intermittent bar-withdrawal type wherein a bar-withdrawal roll spaced from the point of metal freezing is subjected to immediate bar-retracting force effective over a predetermined reverse rotation of the roll when it comes to a standstill at the end of the barwithdrawal motion.

A further object of the present invention is to achieve theabove action in a way that provides ease of adjustment, both as to the amount of the reverse force on the bar and the extent of the reverse movement over which it is exerted, and in such a way that the operation of the apparatus may be visually observed.

A more specific object of the present invention is to provide a continuous casting apparatus of the intermittent bar-withdrawal type including a positive intermittent roll drive mechanism of the oppositely acting cam follower type and wherein predetermined reverse force effective over a predetermined reverse movement is imparted to the bar at the time forward motion of the bar comes to an end, independent of looseness and wear and changes in looseness and wear in the cam apparatus and other drive parts.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof, will best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a general, somewhat diagrammatic view with parts in axial cross-section of a complete continuous casting apparatus of the type to which the present invention is applicable and showing the state of the apparatus at the conclusion of a bar-withdrawal movement;

FIG. 1a is a fragmentary view like FIG. 1 but showing the state of the apparatus at the conclusion of the dwell period;

FIGS. 2 and 3 are views in perspective and in axial cross-section, respectively, of the preferred mechanism for imparting intermittent bar-withdrawal and dwell motions to the roll drive shaft;

FIG. 4 is an elevational view of the bar-withdrawing drive roll and associated mechanism;

FIG. 5 is a side view of the apparatus of FIG. 4 taken along the axis of the drive roll with the parts in the positions taken at the conclusion of the dwell period; and

FIG. 5a is a fragmentary view like FIG. 5 but showing the parts in the positions at the end of the barwithdrawal period.

Referring now to FIG. 1. there is shown at 10 a molten metal holding vessel which, in use, contains a quantity of molten ferrous metal M ready for casting. This vessel is affixed in sealing relation to the mold unit shown generally at 12. This unit has an inlet passage 12a which terminates in a nozzle 12b of boron nitride which intrudes into the path of molten metal and defines an annular end face 12d which is shielded from direct metal flow. The mold has a cylindrical section 120 which is chilled by means not shown. Heat flow to and from the annular downstream face of the exposed boron nitride nozzle is such that molten metal freezes starting at the junction of the outer annular boron nitride face-l2d and the cylindrical inside mold surface 12c so as to progressively form a sleeve-like section 13 having an annular rear face. The cast bar is indicated at 14, FIG. 1. As shown at 14d, bar 14 is solidified at its rear end at the conclusion of a bar-withdrawal operation in a generally annular end face and a generally conical interior, the annular end face having a radius intermediate the radially inboard face of the boron nitride nozzle and the outer exposed radius thereof. A gap 14d exists between the end face and the newly cast section 13 to the rear, this gap being of liquid, or substantially liquid, metal. In FIG. 1 the bar 14 is shown just after a bar-withdrawal movement and at the time dwell commences. As shown in FIG. 1b, the gap 14d welds by the end of the subsequent dwell period, so that the bar is drawn forwardly with the newly cast section affixed on the next withdrawal movement.

At a point spaced from the end of mold 12, the bar 14 passes between drive roll 16 and pinch roll 18. The bite of. these rolls provides a positive engagement be tween drive roll 16 and bar 14 so that the bar partakes of the motion of the roll. The roll 16, as further described hereafter, is driven in a succession of barwithdrawal rotations. Each of these imparts a rapid withdrawal or forward motion to the bar of about three-fourths of an inch. Thereafter, the roll 16 dwells (except for the reversed motion described hereafter) for a time period approximately equal to the time during which bar-withdrawal takes place. Because of the successive movements of the bar, a series of witness marks 14b appear as rings around the bar at spaces equal to the amount of the successive bar-withdrawal motions.

The apparatus of FIG. 1 operates by withdrawing the bar successively in predetermined increments, such as three-fourths of an inch, after which time the section of molten metal that fills the left part of the mold freezes onto the withdrawn end of 14a of the bar. The forward motion is imparted to the bar 14 by the drive roll 16, causing the chilled end 12c of the bar to be drawn away from the nozzle 12d at a more rapid rate than the molten metal freezes. Molten metal thus exists at or near the rear end face of the bar. As the rear end of the bar withdraws and molten metal fills the space behind the bar, the molten metal freezes against the annular face 12d of the nozzle 12b and against the cooled cylindrical face 120 of the mold 12. This action is progressive, beginning at the nozzle end 12b and moving in the forward direction of the bar movement. The rate of barwithdrawal, however, exceeds the rate of molten metal freezing, so that the end face 14a of the bar has molten metal in contact with it or near to it as shown at 14d, FIG. 1. During the subsequent dwell period, the molten metal against the rear end face of the bar solidifies so that by the time the next bar-withdrawal movement takes place. a new sleeve of solid metal extends from the previous end of the bar to the annular face on nozzle 12d and is of sufficient strength to carry the newly solidified section when the bar is next withdrawn. The subsequent withdrawal movement of the bar thus bodily carries the new bar section defined by this sleeve as well as the remainder'of the bar, completing the cycle of operation.

It has been found that the weld between the bar 14 as it exists at the end of each bar-withdrawal movement, and the newly solidified section, if not suitably made, is a source of serious difficulty in carrying out the process. This is the region generally indicated at 14d, FIG. la. If the weld is not effectively made, the solid bar tends to separate from the newly frozen section at this point during the next subsequent barwithdrawal movement. If the weld is not formed and extraction continues it is possible for molten metal to be discharged from the mold onto the foundry floor.

It is believed that the difficulty in forming an effective weld is due to thermal contraction of the bar 14 as it cools. That is, with the roll 16 stationary and the bar cooling, the end becomes withdrawn slightly from the mold 12, inhibitingwelding of the newly formed section to the end of the previously formed bar. In any event, it has been found that a slight reversed movement of the roll 16 can avoid the problem of bar breakage at the point of new weld. Initial attempts to provide such reversed movement, however, resulted in erratic and unpredictable results, especially after a substantial period of operating time. It is belived that this lack of reliability resulted from very slight wearing of the parts of the drive mechanism, wearing that for all normal purposes is incapable of observation. In any event, the improved apparatus described hereafter has served to obviate this difficulty and to permit continuous casting for prolonged periods of time.

Intermittent Roll Drive Mechanism A preferred form of mechanism by which drive roll 16 is actuated in successive bar-withdrawing movements is shown in perspective in FIG. 2. The shaft 20 is driven counterclockwise, as seen in FIG. 2, by a suitable motor (not shown), such as an induction motor. Cams 22 and 24 are keyed to and rotate with the shaft 20. The shaft 26 is connected by suitable gears (not shown) to the bar-withdrawing roll 16. A first cam follower unit indicated generally at 28 is keyed to and drives the shaft 26 and has a series of cam follower rollers 30a, 30b and 300, which are aligned and ride against the cam 22, successively, as described in further detail hereafter. The second cam follower unit indicated generally at 32 is likewise keyed to the shaft 26 a to drive the same. This cam follower similarly carries a series of cam follower rollers 34a, 34b and 340, which are positioned successively to ride against and be engaged by the cam 24.

From the axial cross-sectional view of FIG. 3, it will be apparent that the cam follower roller 30a rides on cam 22 at a position above the line axis x-x joining the axes of shafts 20 and 26. Consequently, cam follower roller 30a drives the shaft 26 in a counterclockwise direction, as seen in FIG. 3, or at least limits the possible clockwise movement of shaft 26 in relation to the shaft 20. It will be further noted that the cam follower roller 34a engages the cam 24 at a point below the line xx joining the axes of shafts 20 and 26. Consequently, the cam follower 34a drives the shaft 26 in the clockwise direction, or at least limits counterclockwise rotation of such shaft in relation to shaft 20.

Cams 22 and 24 are so shaped that the successive positions executed by the shaft 26, on uniform driving rotation of the shaft 20, define a first period, during which time the shaft 26 is advanced progressively (thus pulling the bar out of the mold), and a second period of about the same duration, during which time the shaft 26 is held against rotation and the bar dwells). The mechanical action involved can be seen by tracing the cam shapes illustratively shown in FIG. 3. The shaft 26 rotates one-third turn for each full rotation of shaft 20.

During the course of the foregoing action, the cam follower rollers 30a, 30b and 30c successively engage the cam 22 at points above the line x-x (FIG. 3), and the cam follower rollers 34a, 34b and 340 successively engage the cam 24 at points below the line x-x. The cams 22 and 24 are so shaped that the shaft 26 is positively positioned at all times. That is, with the shaft at any particular position of rotation, the shaft 26 is located by the cams and cam followers at a specific position of rotation. It has been found, however, that there is not only some necessary looseness or lost motion in locating the shaft 26 but, in addition, the apparatus wears in a manner giving rise to unpredictable and varying deviations from the desired position.

The motion imparted to the shaft 26 when the shaft 20 rotates at uniformly angular velocity, includes a first period of about 180 rotation of shaft 20, during which time the shaft 26 rotates in the direction to drive barwithdrawal roll 16 in the bar-withdrawing direction. The amount of such bar-withdrawal motion, as communicated through the drive gears, imparts a barwithdrawal of about three-fourths of an inch. The velocity of rotation progressively increases and then decreases during this period to provide a smooth acceleration and deceleration of the roll 16 and bar 14. During the remainder of a full rotation of the shaft 20, the shaft 26 is driven in a slight reversed motion. The magnitude of this rotation is sufficient to provide, at the roll 16, a reversed motion on the bar at roll 16. The amount of such rotation may, for exmaple, be about twenty-fivethousandths of an inch, although this figure may be more or less in accordance with the particular installation.

The Instantaneous Reverse Force Applying Mechanism The mechanism for applying an instantaneous reverse force to the bar 14 at the moment dwell starts is shown in FIGS. 4, 5 and 5a. As seen best in FIG. 4, the roll 16 which drives the bar 14 has an extension attached by bolts 36a and forming inner sleeve bearing member 360. This member has an integral flanged portion 36b, which in turn receives the securing bolts 38, FIGS. 4 and 5, which secure the disc brake member 40 rigidly thereto. The outer sleeve bearing member 42, FIG. 4, is affixed to the upstanding support panel 43.

The disc brake rotor member 40 forms one part of a two-part brake mechanism, the other part being the caliper or shoe unit indicated generally at 44, FIGS. 4, 5 and 5a. This caliper is of conventional automotive disc brake construction and includes a housing unit which is affixed to the carriage 44b by bolts 44c. The carriage 44b is pendulously supported from the sleeve bearing member and the extending stub 36d of shaft 36 by the hanger 44d, which is carried by the sleeve bearing 44e and also supported by sleeve bearing 42 and support panel 43. The carriage 44b further has a horizontal crossplate 44f which in turn carries the depending stop ear 44g. It will be observed that the entire brake part 42, 43, 44 to 44g, inclusive, is a structure which, upon brake application, tends to rotate in unison with the shaft 16 and stub shaft 36, unless such rotation is limited to stop elements engaging the ear 44g.

The housing 44a of brake caliper 44 defines a cylinder 4411, FIG. 5, which in turn receives piston 44j. Fluid pressure is exerted on the back face of the piston 44j through the fluid connection fitting 44k, FIG. 5, provided for the purpose. A pair of brake shoes 44m, FIGS. 4 and 5, straddle the disc 40 and are pressed into frictional braking engagement therewith by the fluid pressure applied through fitting 44k and exerted against the rear face of piston 44j. In the normal use of the apparatus herein described, a predetermined constant fluid pressure is applied so as to give predetermined constant brake resistance to rotation of the disc 40.

A support plate 46, FIGS. 4, 5 and 5a, is mounted on the machine frame (not shown) by the bolts 460, FIG. 5. The plate 46 carries an adjustable bar retracting stop unit indicated generally at 48, FIGS. 5 and 5a. This stop unit includes an outwardly extending support plate 4811 which threadedly receives the adjustable horizontally oriented stop screw 48b. This screw is held in adjusted position by jam nut 480. It will be evident that the stop screw 48b engages the ear 44g of the brake part 44 to limit rocking of the brake part in the counterclockwise direction, as seen in FIG. 5.

A fixed stop unit indicated generally at 52, FIGS. 4, 5 and 5a, includes a sleeve 520, which is affixed to the support plate 46 in generally aligned relation to the stop screw 48!). This sleeve has a threaded end 52b, a smaller diameter cylindrical bore 520 and an end face 52d, having a detent-receiving opening 52e. Detent 54 is disposed within the bore 52c and has its end 54a extending through the opening 52e, as shown in FIGS. 5 and 5a. An annular shoulder 54b on the detent 54 receives compression springs 56 and 58 on its back side, and on its forward side overlays the margins of opening 52e. Springs 56 and 58 are adjustably compressed by the screw 60 which is in threaded engagement with the threaded end 52b of sleeve 52. .lam nut 60a holds the screw 60 in adjusting position. As shown in FIG. 5, when the roll 16 is rotated in a counterclockwise direction, as seen in that figure, the ear 44g engages stop 48 and the detent 54 extends outboard stop face 52d to engagement with the opposite face of the ear. When the roll 16 and stub shaft 36b rotate in the clockwise direction, as seen in FIG. 5, the detent 54 is first depressed against the compression springs 56 and 58 by the ear 44g until the position as shown in FIG. 5a is reached. Thereafter, the end face 52d engages ear 44g and serves as a fixed stop to limit further clockwise rotation of the brake unit 44.

The above apparatus is adjusted for operation by first setting the stop screw 48b to permit back and forth motion of the ear 44g between stop face 52d and stop screw 48b substantially equal to two times the desired reverse motion of the bar during the dwell period. For example, with a bar-withdrawal motion of about threefourths of an inch, the initial adjustment of the screw 48b might be about 0.050 inch, which produces about 0.025 inch reverse movement of the bar 14 at roll 16. The bias applied by springs 56 and 58 is adjusted by screw 60 at a value sufficient to exert a reverse force on the ear 52d with the detent depressed as in FIG. a. A force of about 450 pounds has been used in practice. The fluid pressure applied to the brake-applying piston 44j via fitting 44k is then chosen at a value producing a brake slip torque somewhat greater than the torque produced by the springs 56 and 58. It has been found that these adjustments are not critical and the brake pressure, spring compression, and the setting of the fixed stop can be varied considerably without precluding the effective and reliable continuous casting operation characteristic of the present invention, but it is critical to have the brake and associated parts present and operative as described above.

it is not known why the apparatus of the present invention is effective to the surprising extent that it is. lt is believed, however, that this is the consequence of the instantaneous application, effective over a limited reverse bar movement, of reverse torque to the roll 16 at the instant the forward velocity of the roll falls to zero at the end of the bar-withdrawal stroke. During the barwithdrawing rotation of the roll 16, the cam 24 drives the roll forwardly via the cam follower 340 (or, on successive strokes, cam followers 34b and 34c) and the intermediate gearing provided between shaft 26 and the roll 16. The forward lost motion or slack in the system is taken up at this time. After the peak forward velocity is reached, the earns 22 and 24 coact with their respective followers to provide either forward or reverse torque on shaft 26, depending on inertia effects and frictional resistance to rotation, and lost motion. The brake friction applied to disc 40 (and hence to the roll 16) is one component of the frictional resistance. At some point in time the total decelerating forces bring the roll 16 and bar 14 to a standstill, at which instant the ear 44g is in the position shown in FIG. 5a. The springs 56 and 58 now immediately exert a reverse torque on the roll 16 via the frictional engagement of shoes 44m and the disc 40. The brake resistance is sufficient to transmit this torque without slip, so that the bar 14 is subjected to the reverse torque due to these springs without any time delay. This torque continues to be applied through the subsequent reverse movement of the bar corresponding to the adjustment of the stop screw 48b, FIGS. 5 and 5a. When the ear 44g seats against the stop screw 48b, however, the brake force, which up to this time tends to transmit reverse force to the bar, is now a resistive force and opposes further reversed bar movement. During all of this action the cams 22 and 24, acting through the respective cam followers and with some amount of lost motion, drive the shaft 26 in a slight reversed motion, and the shaft 26, again acting with some amount of lost motion, tends to drive roll 16 slightly in the reversed direction. The net effect is to apply force and cause movement of the roll 16 in a manner that has been found to provide reliable welding of each new bar section to the previously formed end of the bar, resulting in effective continuous casting.

While we have shown and described a specific embodiment of the present invention, it will, of course, be apparent that various modifications and alternative constructions may be used without departing from the true spirit and scope thereof. We therefore intend by the appended claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What is claimed is:

1. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and withdrawn by a roll spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination:

means to impart successive forward bar-withdrawing rotations to the roll to withdraw the bar in said forward steps, said means being characterized by inevitable and variable lost motion effects;

a two-part mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being mounted for movement in unison with the first part under brakeengaging action, the other part defining faces which move forward and backward, respectively, as the roll withdraws or retracts the bar;

a fixed stop in the path of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest travel of said other part in response to the brake action;

an adjustable stop in the path of the backward facing face when the roll rotates in the direction of reversed movement of the roll, and effective to fix adjustably the travel of the said other part in the reverse direction;

and a resilient element effective to resist travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having force less than the brake force so that (a) during forward stroke the resilient element yields until the fixed stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roll through the brake, and (c) when reversed roll movement causes seating against the adjustable stop, the brake action resists further reversed movement.

2. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and is withdrawn by a roll spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination:

means to impart successive forward bar-withdrawing rotations to the roll to withdraw the bar in said forward steps, said means being characterized by inevitable and variable lost motion effects;

a two-part brake mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being mounted for movement in unison with the first part under brake-engaging action, the other part defining faces which move forward and backward, respectively, as the roll withdraws or retracts the bar;

a first stop in the path of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest travel of said other part in response to the brake action;

a second stop in the path of the backward facing face when the roll rotates in the direction of reversed movement of the roll, one of said stops being adjustable and effective to fix adjustably the travel of the said other part in the reverse direction;

and a resilient element effective to resist travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having force less than the brake force so that (a) during forward stroke the resilient element yields until the first mentioned stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roll through the brake, and (c) when reversed roll movement causes seating against the second mentioned stop, the brake action resists further reversed movement.

3. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and is withdrawn by a roll spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination:

means to impart successive forward bar-withdrawing rotations to the roll to withdraw the bar in said forward steps, said means being characterized by inevitable and variable lost motion effects;

a two-part brake mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being mounted for movement in unison with the first part under brake-engaging action, the other part defining faces which move forward and backward, respectively, as the roll withdraws or retracts the bar;

a first stop in the path of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest travel of said other part in response to the brake action;

a second stop in the path of the backward facing face when the roll rotates in the direction of reversed movement of the roll, and effective to fix the travel of the said other part in the reverse direction;

and a resilient element effective to resist travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having force less than the brake force so that (a) during forward stroke the resilient element yields until the first mentioned stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roll through the brake, and (c) when reversed roll movement causes seating against the second mentioned stop, the brake action resists further reversed movement.

4. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and is withdrawn by a roll spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements,

and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination:

a first shaft driven at uniform angular velocity;

a second shaft in driving connection with the roll;

an intermittent drive for said second shaft from the first shaft including forward and reverse cam and follower elements effective to impart successive forward bar-withdrawing rotation to the second shaft and intervening dwell periods to the same, the second shaft having a reversed rotation of small amount in relation to the forward rotation during the dwell period;

a two-part brake mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being mounted for movement in unison with the first part under brake-engaging action, the other part defining faces which move forward and backward, respectively, as the roll withdraws or retracts the bar;

a first stop in the path of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest travel of said other part in response to the brake action;

a second stop in the path of the backward facing face when the roll rotates in the direction of reversed movement of the roll, and effective to fix the travel of the said other part in the reverse direction;

and a resilient element effective to resist travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having force less than the brake force so that (a) during forward stroke'the resilient element yields until the first mentioned stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roller through the brake, and (c) when reversed roller movement causes seating against the second mentioned stop, the brake action resists further reversed movement.

5. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and is withdrawn by a roll having an axis and spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination:

means to impart successive forward bar-withdrawing rotations to the roll to withdraw the bar in said forward steps, said means being characterized by inevitable and variable lost motion effects;

a two-part brake mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being pendulously suspended for swinging movement in relation to the axis of the roll and in unison with the first part under brake-engaging action, the other part defining faces which swing forward and backward, respectively, about the axis of the roll as the roll withdraws or retracts the bar;

a first stop fixedly supported in the path of swing of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest swinging travel of said other part in response to the brake action;

a second stop fixedly supported in the path of swing of the backward facing face when the roll rotates in the direction of reversed movement of the roll, one of said stops being adjustable and effective to fix adjustably the swinging travel of the said other part in the reverse direction;

and a resilient element effective to resist swinging travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element action resists further reversed movement. 

1. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and withdrawn by a roll spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during thE dwell period, the mechanism comprising in combination: means to impart successive forward bar-withdrawing rotations to the roll to withdraw the bar in said forward steps, said means being characterized by inevitable and variable lost motion effects; a two-part mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being mounted for movement in unison with the first part under brake-engaging action, the other part defining faces which move forward and backward, respectively, as the roll withdraws or retracts the bar; a fixed stop in the path of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest travel of said other part in response to the brake action; an adjustable stop in the path of the backward facing face when the roll rotates in the direction of reversed movement of the roll, and effective to fix adjustably the travel of the said other part in the reverse direction; and a resilient element effective to resist travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having force less than the brake force so that (a) during forward stroke the resilient element yields until the fixed stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roll through the brake, and (c) when reversed roll movement causes seating against the adjustable stop, the brake action resists further reversed movement.
 2. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and is withdrawn by a roll spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination: means to impart successive forward bar-withdrawing rotations to the roll to withdraw the bar in said forward steps, said means being characterized by inevitable and variable lost motion effects; a two-part brake mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being mounted for movement in unison with the first part under brake-engaging action, the other part defining faces which move forward and backward, respectively, as the roll withdraws or retracts the bar; a first stop in the path of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest travel of said other part in response to the brake action; a second stop in the path of the backward facing face when the roll rotates in the direction of reversed movement of the roll, one of said stops being adjustable and effective to fix adjustably the travel of the said other part in the reverse direction; and a resilient element effective to resist travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having force less than the brake force so that (a) during forward stroke the resilient element yields until the first mentioned stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roll through the brake, and (c) when reversed roll movement causes seating against the second mentioned stop, the brake action resists further reversed movement.
 3. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and is withdrawn by a roll spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination: means to impart successive forward bar-withdrawing rotations to the roll to withdraw the bar in said forward steps, said means being characterized by inevitable and variable lost motion effects; a two-part brake mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being mounted for movement in unison with the first part under brake-engaging action, the other part defining faces which move forward and backward, respectively, as the roll withdraws or retracts the bar; a first stop in the path of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest travel of said other part in response to the brake action; a second stop in the path of the backward facing face when the roll rotates in the direction of reversed movement of the roll, and effective to fix the travel of the said other part in the reverse direction; and a resilient element effective to resist travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having force less than the brake force so that (a) during forward stroke the resilient element yields until the first mentioned stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roll through the brake, and (c) when reversed roll movement causes seating against the second mentioned stop, the brake action resists further reversed movement.
 4. A continuous casting apparatus for ferrous metal of the type wherein the bar issues in solid form from a fixed mold and is withdrawn by a roll spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination: a first shaft driven at uniform angular velocity; a second shaft in driving connection with the roll; an intermittent drive for said second shaft from the first shaft including forward and reverse cam and follower elements effective to impart successive forward bar-withdrawing rotation to the second shaft and intervening dwell periods to the same, the second shaft having a reversed rotation of small amount in relation to the forward rotation during the dwell period; a two-part brake mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being mounted for movement in unison with the first part under brake-engaging action, the other part defining faces which move forward and backward, respectively, as the roll withdraws or retracts the bar; a first stop in the path of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest travel of said other part in response to the brake action; a second stop in the path of the backward facing face when the roll rotates in the direction of reversed movement of the roll, and effective to fix the travel of the said other part in the reverse direction; and a resilient element effective to resist travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having force less than the brake force so that (a) during forward stroke the resilient element yields until the first mentioned stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roller through the brake, and (c) when reversed roller movement causes seating against the second mentioned stop, the brake action resists further reversed movement.
 5. A continuous casting apparatus for ferrous metal of the type wheRein the bar issues in solid form from a fixed mold and is withdrawn by a roll having an axis and spaced from the point of freezing of the bar in a succession of forward step movements separated by periods of dwell comparable in time to the time of the forward movements, and in which a slight reversed movement is imparted to the bar at the point of roll engagement during the dwell period, the mechanism comprising in combination: means to impart successive forward bar-withdrawing rotations to the roll to withdraw the bar in said forward steps, said means being characterized by inevitable and variable lost motion effects; a two-part brake mechanism in constant engagement, one part being rigidly affixed to and rotatable with the roll and the other part being pendulously suspended for swinging movement in relation to the axis of the roll and in unison with the first part under brake-engaging action, the other part defining faces which swing forward and backward, respectively, about the axis of the roll as the roll withdraws or retracts the bar; a first stop fixedly supported in the path of swing of the forward facing face when the roll rotates in the bar-withdrawing direction, and effective to arrest swinging travel of said other part in response to the brake action; a second stop fixedly supported in the path of swing of the backward facing face when the roll rotates in the direction of reversed movement of the roll, one of said stops being adjustable and effective to fix adjustably the swinging travel of the said other part in the reverse direction; and a resilient element effective to resist swinging travel of the said other part in response to roll rotation in the bar-withdrawing direction, said element having torque less than the brake torque so that (a) during forward stroke the pendulously suspended other part swings as the resilient element yields until the first mentioned stop is engaged and thereafter the brake slips, (b) when forward bar motion ceases, the resilient element instantaneously applies reverse torque to the roll through the brake, and (c) when reversed roll movement causes seating against the second mentioned stop, the brake action resists further reversed movement. 